The object of this proposal is the study at the single cell level of mechanisms underlying the interaction between tritium labelled antigen and antigen receptor sites. This includes the detailed investigation by radioautography of changes in the surface distribution of antigen-receptor complexes on mouse lymphocytes during immunity and tolerance induction. The first series of experiments is concerned with the immunological significance of the receptor capping phenomenon. In addition there will be an investigation of the apparently close functional relationship between receptors for phytomitogens (e.g. Concanavalin-A) and those for antigen (e.g. tritium labelled polymerized flagellin). Attention will be paid to thymus dependent cellular mechanisms whereby Con-A inhibits immune induction and influences antigen-receptor capping. These studies will be extended to the use of basic brain protein and synthetic peptides identical with antigens on basic protein, with the aim of elucidating some of the problems related to "self" tolerance and autoimmunity. A second experimental series is concerned with the physico-chemical state of the lymphocyte membrane as it relates to the control of antigen receptor site aggregation.